bpo-43413: Fix handling keyword arguments in subclasses of some buitin classes (GH-26456)

* Constructors of subclasses of some buitin classes (e.g. tuple, list,
  frozenset) no longer accept arbitrary keyword arguments.
* Subclass of set can now define a __new__() method with additional
  keyword parameters without overriding also __init__().

1 files changed, 27 insertions, 0 deletions

diff --git a/Lib/test/test_tuple.py b/Lib/test/test_tuple.py
index d2a2ed3..9ce80c5 100644
--- a/Lib/test/test_tuple.py
+++ b/Lib/test/test_tuple.py
@@ -42,6 +42,33 @@ class TupleTest(seq_tests.CommonTest):
         with self.assertRaisesRegex(TypeError, 'keyword argument'):
             tuple(sequence=())
 
+    def test_keywords_in_subclass(self):
+        class subclass(tuple):
+            pass
+        u = subclass([1, 2])
+        self.assertIs(type(u), subclass)
+        self.assertEqual(list(u), [1, 2])
+        with self.assertRaises(TypeError):
+            subclass(sequence=())
+
+        class subclass_with_init(tuple):
+            def __init__(self, arg, newarg=None):
+                self.newarg = newarg
+        u = subclass_with_init([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_init)
+        self.assertEqual(list(u), [1, 2])
+        self.assertEqual(u.newarg, 3)
+
+        class subclass_with_new(tuple):
+            def __new__(cls, arg, newarg=None):
+                self = super().__new__(cls, arg)
+                self.newarg = newarg
+                return self
+        u = subclass_with_new([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_new)
+        self.assertEqual(list(u), [1, 2])
+        self.assertEqual(u.newarg, 3)
+
     def test_truth(self):
         super().test_truth()
         self.assertTrue(not ())